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capable of providing a PC-like experience over the wire. Still, these protocols may run into trouble when delivering rich media to virtual desktops.

One of the biggest challenges with desktop virtualization is providing enough bandwidth and low-latency connectivity for these protocols to deliver the same quality of experience as if the user were connected to the LAN. The majority of remote display protocols progressively degrade the user experience to fit sessions into the available bandwidth.

Even with recent protocol enhancements, some media react negatively to remote display protocols when there isn't enough bandwidth to keep up with the rapid frame rates of modern video. Many users report lags between the video and audio, which can leave them feeling as though they're watching a poorly dubbed kung fu movie from the 1970s.

That's where media content redirection comes in. To help you give users the best experience, let's review the latest changes to rich-media delivery methods from desktop virtualization vendors.

More on remote display and rich media

For example, the content redirection feature can detect that a user is watching a video and then redirect the video so it's delivered directly to the user's device by using that device's native coder/decoder (codec) support for streaming rich media. The user gets the impression that everything is happening within the virtual desktop when, in fact, the virtual desktop and the client device are working together to render the user experience.

Not all virtual desktop vendors support the media content redirection functionality. Some vendors remain committed to delivering the entire user experience via the virtual desktop -- with no client dependencies except for their virtual desktop client. Such organizations believe that the client should not need any special software for virtual desktop infrastructure (VDI) to function. Customers who adopt the zero-client approach should be aware that media content redirection has client-side requirements that render it inapplicable to them.

Other vendors, such as VMware, have continued to offer tuning capabilities within their management software. These features allow the administrator to have more granular control over video software like Adobe Flash. The settings appear on the properties of any desktop pool within the View Administration portal.

These settings also allow IT admins to degrade the overall quality of the user experience to conserve bandwidth and to adjust the frame rate of a Flash video. The lower the frame rate, the fewer changes are allowed in the video, reducing the bandwidth consumed. It is possible to degrade the Adobe Flash experience without the user noticing a difference. YouTube videos, for instance, are often encoded in a lossy format anyway.

There have also been advances in graphics processing units and server offload cards, such as Teradici's APEX 2800. The concept is to take the load that rendering pixels and codec generate away from the onboard CPUs and instead have these processed by dedicated card. This can significantly improve the virtual desktop user experience with rich media.

Once the virtualization host has been fitted with acceleration cards, the administration tools can offer different levels of performance to different desktop pools within the management layer (Figure 1).

Specify performance levels for different desktop pools.

Rich media on virtual desktops isn't restricted to videos on YouTube. This term also applies to any media on the local client device, such as USB-based memory sticks, and input devices such as Dictaphones and scanners.

Most virtual desktop vendors support the redirection of client devices so that although a USB device may appear in the virtual desktop, when a user saves files to it, those files are sent back to the user's client device, wherever it is located. This requires additional bandwidth and is often included as a virtual channel within the remote display protocol.

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